1. Field of the Invention
The present invention generally relates to isolating RF signals and, more particularly, to isolating RF signals with optical modulation.
2. Description of the Related Art
For RF signals in the microwave frequency range and higher, traditional electronic techniques for isolation between RF paths have been limited. Methods have been investigated to improve the isolation by using either multiple circulators or matched pairs of circulators with antennas. Photonic techniques provide multiple advantages over electronic techniques, one of them being large instantaneous bandwidths. A photonic solution to RF isolation would allow for increased bandwidths and higher isolation over electronic techniques. The use of a bi-directional signal interface has been demonstrated using an optical modulator for transmit and receive functions. Further work has been shown to use this system with high isolating between the RF transmit and RF receive ports. One method for transporting RF signals over a photonic link involves single-side-band modulation. By using single side band modulation, a previous demonstration has shown that two different RF signals can be single side band modulated such that one signal is on the opposite side of the optical carrier than the other signal. Further demonstrations have shown multiple signals can be placed on either side of the optical carrier, as well as mixing baseband and microwave signals on either side of the carrier.
Even with the work done in this area, there is a need in the art for better methods of isolating RF signals.